vis: add workaround for broken color handling in Terminal.app

Terminal.app sets $TERM=xterm-256color and ships a corresponding
terminfo description advocating that it is capable of color changes
to the 256 color palette when in fact it can not.

We introduce a new boolean option "change-256colors" which is
true by default but can be used to disable color changes. It is
automatically set if Terminal.app is detected using $TERM_PROGRAM.

This should fix display artifacts as described in #456.

1 files changed, 7 insertions, 0 deletions

diff --git a/sam.c b/sam.c
index 95b2690..b232726 100644
--- a/sam.c
+++ b/sam.c
@@ -302,6 +302,7 @@ enum {
 	OPTION_COLOR_COLUMN,
 	OPTION_HORIZON,
 	OPTION_SAVE_METHOD,
+	OPTION_CHANGE_256COLORS,
 };
 
 static const OptionDef options[] = {
@@ -385,6 +386,12 @@ static const OptionDef options[] = {
 		OPTION_TYPE_STRING, OPTION_FLAG_WINDOW,
 		"Save method to use for current file 'auto', 'atomic' or 'inplace'",
 	},
+	[OPTION_CHANGE_256COLORS] = {
+		{ "change-256colors" },
+		OPTION_TYPE_BOOL, OPTION_FLAG_NONE,
+		"Change 256 color palette to support 24bit colors",
+	},
+
 };
 
 bool sam_init(Vis *vis) {